In several situations, a certain area is reserved for one-way traffic only. For example, at an entrance to a sporting event or an entrance of a secure area. A person not following the one-way traffic can avoid paying the entry fees, or more dangerously, can compromise security at, for example, an airport. Preventing such activity is of great importance.
Traditionally, two approaches are used to prevent a person from moving in such a wrong direction: a physical barrier or a security guard. A physical barrier is typically some sort of a turnstile (e.g., at a sporting event, or at a subway station), or a tire shredding spike strip at a parking lot. The problem with these solutions is that they considerably slow down the traffic flow and have problems accommodating special needs, like wheelchairs or suitcases. For these reasons some locations, like airports, typically use the second approach and employ one or more security guards to watch for and prevent people proceeding in the wrong direction (e.g., at an exit corridor). The problem with this second approach is that a security guard can become distracted or bored, allowing a person to proceed in the wrong direction.
Video surveillance systems are in common use today. Traditional video surveillance systems generally involve the use of one or more video cameras, and the video output from the camera(s) is either recorded for later review or monitored by a human observer, or both. Some video surveillance systems use computer-based video processing techniques to detect various events, providing unobtrusive, 24/7 vigilance (i.e., 24 hours a day, 7 days a week). Examples of such systems are discussed in the following, for example, which are incorporated herein by reference: U.S. patent application Ser. No. 09/987,707, filed Nov. 15, 2001, titled “Video Surveillance System Employing Video Primitives”; U.S. patent application Ser. No. 09/972,039, filed Oct. 9, 2001, titled “Video Tripwire”; Third Generation Surveillance Systems, Proceedings of the IEEE, October 20001.